The present invention generally relates to devices for conveying lightweight sheet stock items (such as sheets of paper, photos, transparencies, etc.) in a sheet handling path by means of streams or blasts of air. More particularly, this invention relates to devices for individually withdrawing such sheets from a stack, conveying them to a work station (scanner, photocopier, printing device and the like), removing said sheets from that work station and depositing them at some other location in the sheet handling path (e.g., at a sheet collection tray).
Some prior art sheet handling machines have employed blowers to produce air streams, positive air jets and negative vacuum streams that, in some way, handle sheet stock materials. For example, U.S. Pat. No. 4,768,769 teaches a paper feeding apparatus having a paper support tray, a rear vacuum plenum chamber (that acquires and physically contacts with the rear portion of a sheet of paper that is part of a vertical stack of said paper) and a front vacuum plenum chamber that is positioned over the front of the top sheet of that stack. The front vacuum is especially adapted to acquire and physically contact with the front portion of such a sheet. A sheet transport device is associated with the front vacuum plenum in order to transport a sheet that has been separated from the top of the stack and move it in a forward direction.
This sheet handling machine also employs an air knife positioned at the rear of the vertical stack. The air knife injects air between the trailing edge of the top sheet of paper in the vertical stack and the remainder of that stack. Again, after the sheet is separated from the stack by the air knife, it is acquired by, and physically contacted with, the front vacuum plenum and then transported in a forward direction. As the trailing edge of the removed sheet clears the vacuum, the next sheet in the vertical stack is, likewise, pried from the stack by the air knife. The air knife includes preacquisition fluffer jets that initially loosen the top few sheets in the stack. The device also employs lateral converging air streams to facilitate separation of the uppermost sheet from the stack.
U.S. Pat. No. 4,579,330 teaches a pneumatic sheet feeder for removing individual sheets (such as sheets of paper) from a vertical stack. A pair of parallel guide rails are provided so that the vertical stack is confined between the guide rails. This assures movement in a defined direction. Air blast nozzles are provided in the guide rails for blowing air streams against the stack to form an air cushion between the lowest sheet in the stack and the sheets above it. Radial openings in a suction chamber cause suction induced adhesion of the leading edge of the lowermost sheet with a vacuum producing cylinder so that, upon rotation of said cylinder, the lowermost sheet is carried away from the bottom of the stack.
Many air stream employing sheet feeder devices are, however, inclined to suffer from misfeeds wherein two or more sheets are withdrawn from a vertical stack from which only one sheet should be withdrawn for individual delivery to a work station. Such two or more misfed sheets can be fully registered or partially registered with each other as they are withdrawn from the stack. Such misfeeds are annoying, mistake producing, expensive and sometimes even destructive to certain sensitive, high speed equipment such as printers, scanners, photocopiers, etc.
Hence, applicant""s invention is especially concerned with separating a top sheet (e.g., of paper) from a stack with less chance of misfeeds of the type just noted. In order to do this, the sheet feeding apparatus of this patent disclosure uses a sheet stepping device that places said sheets in a staircase-like configuration and then uses air nozzles to separate a top sheet from the staircase stacked sheets. An air stream created by such nozzles also establishes an air cushion between the top sheet and the other sheets. This air stream conveys the top sheet to a work station. In some of the more preferred embodiments of this invention, the same air stream used to separate the top sheet from the remainder of the stack is used to convey said sheet towards the work station.
The present invention solves many of the prior art misfeed problems associated with pneumatic separation of a top sheet of a stack of sheet material (such as a stack of paper, photos, transparencies and the like). It does this by first placing the vertical stack of sheet stock in a staircase configuration. In such a staircase configuration, the top sheet has been mechanically loosened from the sheet immediately under it by a staircasing action and placed in position to be moved forward by a stream of air delivered to the rear side of the top sheet. The second or next lower sheet in the stack, and all of the sheets below it, are held down by a holding force delivered to the top rear side of the second sheet in the stack by a hold down device. Thus the second uppermost sheet in the stack, and all of the sheets under it, are held in place in the face of the air stream that is aimed at the rear side of the top sheet in the stack. Aside from impinging on the rear side of the top sheet in the stack, this air stream also forces its way under said top sheet and, in effect, creates a moving air cushion between the underside of the top sheet and the top side of the second sheet (that is being held down by the sheet hold down device).
Consequently, the air stream pries the top sheet from the stack (without disturbing the other sheets in the staircased stack) and then conveys said top sheet in a forward direction toward a work station. This stream of air carries the top sheet into a sheet acquisition tunnel which defines a space in which the air stream, and the sheet of paper it carries, are confined and which leads to (or at least toward) a downstream work station. The work station is provided with a stop upon which the leading edge of the sheet being conveyed by the air stream impinges. This impingement causes the sheet to drop, under the influence of gravity (or by mechanical means such as downwardly directed air streams), to a defined working position at a work station. To aid in this dropping action, the cushioning air stream may be momentarily stopped and/or diverted to another path by air flow control valves or air stream diverting surfaces. The sheet is then operated upon at the work station. For example, in the case of a sheet of paper, the underside of the sheet of paper can be xe2x80x9cread fromxe2x80x9d or xe2x80x9cwritten toxe2x80x9d in ways well known to the paper scanning, photocopying and printing arts. At the end of such operations (reading and/or writing), the sheet is lifted from the work station by blasts of air delivered to the underside and/or edge regions of said sheet. Upon being lifted to an elevation sufficient to clear the top of the work station, the sheet is again placed in an air stream which carries it to its next destination in a sheet handling path to be followed by that sheet. In some of the more preferred embodiments of this invention, the air stream that carries the sheet from the work station emanates from the same nozzle that originally pried the sheet from the staircased stack and delivered it to the work station.
The next destination in the sheet handling path can be a final destination wherein the sheet is delivered to a tray where it is vertically stacked upon previously delivered sheets. In the alternative the sheet can be delivered to another work station in the sheet handling path. In some of the more preferred embodiments of this invention, the air stream employed to (1) pry a top sheet from a stack, (2) convey that top sheet to a work station, (3) carry that sheet away from the work station and (4) deposits that sheet at some intermediate point or end point in the sheet handling process can, each, be aided by various air flow conveying tunnels, auxiliary air nozzles, sheet guide rails and sheet stopping devices hereinafter more fully described.